New paleomagnetic data show no Mesozoic rotation of the Corsica-Sardinia microplate

Abstract

The paleogeography and tectonic history of the Corsica-Sardinia Microplate (CSM) and the opening of the Liguro-Provençal ocean since Oligocene times is based on a wealth of geologic, geophysical, and paleomagnetic studies and relatively well understood. From Neogene paleomagnetic data it is known that the CSM rotated ~55° counterclockwise (CCW). Conversely, the paleogeography of Sardinia and the surrounding regions during the Mesozoic is much less clear due to the absence of paleomagnetic data, except for scarce studies on Triassic and Jurassic sediments from Sardinia. These data indicate a ~90° CCW rotational history of the microcontinent. So, between the Mesozoic data and the Neogene data is an rotational gap of ~35°. Earlier studies confirm the structural coherence of Sardinia from the Late Paleozoic. This study attempts to contribute to better time constraints for tectonic motions of the CSM and determine whether the CSM was part of a bigger plate. A total of ~500 oriented core samples from 1 Triassic site, 2 Jurassic sites and 2 Cretaceous sites have been collected from the Nurra region. Samples taken from the Jurassic of Nurra proved to be too weakly magnetized and did not yield any stable directions. The Cretaceous results of one site did not yield high quality data due to weak magnetization and consequently insufficient sampling. The Triassic site yielded a characteristic remanent magnetisation (ChRM) of D= 297°, I= 38°, which is in good agreement with earlier published Triassic data. Reliable Cretaceous data from Coniacian-Santonian rocks yielded a ChRM of D= 277°, I= 49°. No significant rotation of Sardinia with respect to Europe is observed between the Anisian (245.0 Ma) and the Santonian (83.5 Ma). The Nurra region and the Iberian sub-continent do not share an apparent polar wander path. This implies that Sardinia was in the Cretaceous not a part of Iberia, contrary to earlier suggestions. In the Coniacian-Santonian no rotation with respect to Europe is observed, therefore first stage of rotation must have occurred later, between 85.8 Ma and 40.4 Ma.